A fine idea to save water.. You could use a battery pump,, a 120vac pump,, or ideally a hand pump. Icarus
To take a slightly different angle: Why is she still bathing a 6-year old? She says that is taking 30 gallons of water. With a 7 minute shower and a 1.5 gpm shower head she could cut that by 19.5 gallons/day, over 7,000 gallons/year. Even a 10 minute shower with a low flow head would cut that water usage in half. I agree with Icarus though, it would be easier to build your own for something like this. I would also probably want to run gray water through soil/sand/gravel column to filter out soaps and nasty bacteria before I put that water in a food producing garden. I wouldn't worry about it as much on the lawn...
Also, the link in the article itself is wrong, it should be H2ouse.org : Take Action (They had it listed as .com and they used a zero instead of an "o" which resulted in a dead link.)